A variety of Clostridium sp. that secrete neurotoxic toxins have been discovered since 1890s, and the characterization of toxins that are secreted from these bacteria has been made for the past 70 years (Schant, E. J. et al., Microbiol. Rev., 56:80, 1992).
Neurotoxic toxins derived from the Clostridium sp., that is, botulinum toxins, are classified into seven serotypes (types A to G) depending on their serological properties. Each of the toxins has a toxin protein having a size of about 150 kDa and naturally comprises a complex of several non-toxic proteins bound thereto. A medium complex (300 kDa) is composed of a toxin protein and a non-toxic non-hemagglutinin protein, and a large complex (450 kDa) and a very large complex (900 kDa) are composed of the medium-sized complex bound to hemagglutinin (Sugiyama, H., Microbiol. Rev., 44:419, 1980). Such non-toxic hemagglutinin proteins are known to function to protect the toxin from low pH and various proteases in the intestines.
The toxin is synthesized as a single polypeptide having a molecular weight of about 150 kDa in cells, and then cleaved at a position of ⅓ starting from the N-terminal end by the action of intracellular protease or treatment with an artificial enzyme such as trypsin into two units: a light chain (L; molecular weight: 50 kDa) and a heavy chain (H; molecular weight: 100 kDa). The cleaved toxin has greatly increased toxicity compared to the single polypeptide. The two units are linked to each other by a disulfide bond and have different functions. The heavy chain binds to a receptor of a target cell (Park. M. K. et al., FEMS Microbiol. Lett., 72:243, 1990) and functions to interact with a biomembrane at low pH (pH 4) to form a channel (Mantecucco, C. et al., TIBS., 18:324, 1993), and the light chain has the pharmacological activity of interfering the secretion of neurotransmitters, when it is permeable to cells by using detergent or introduced by electroporation or etc (Poulain, B. et al., Proc. Natl. Acad. Sci. USA., 85:4090, 1988).
The toxin inhibits the exocytosis of acetylcholine at the cholinergic presynapse of a neuromuscular junction to cause asthenia. It has been considered that even treatment with a very small amount of the toxin exhibits toxicity, suggesting that the toxin has any enzymatic activity (Simpson, L. L. et al., Ann. Rev. Pharmacol. Toxicol., 26:427, 1986).
According to a recent report, the toxin has metallopeptidase activity, and its substrates include composed of synaptobrevin, syntaxin, a synaptosomal associated protein of 25 kDa (SNAP25), etc., which are the unit proteins of an exocytosis machinery complex. Each type of toxin uses one of the above-described three proteins as its substrate, and it is known that type B, D, F and G toxins cleave synaptobrevin at a specific site, type A and E toxins cleave SNAP25 at a specific site, and type C cleaves syntaxin at a specific site (Binz, T. et al., J. Biol. Chem., 265:9153, 1994).
Particularly, type A botulinum toxin is known to be soluble in a dilute aqueous solution at a pH of 4.0-6.8. It is known that a stable non-toxic protein is separated from neurotoxin at a pH of about 7 or higher, and as a result, the toxicity is gradually lost. Particularly, it is known that the toxicity decreases as pH and temperature increase.
The botulinum toxin is fatal to the human body even in small amounts and is easy to produce in large amounts. Thus, it constitutes four major bio-terror weapons together with Bacillus anthracis, Yersinia pestis and smallpox virus. However, it was found that, when type A botulinum toxin is injected at a dose that does not systematically affect the human body, it can paralyze local muscle in the injected site. Based on this characteristic, type A botulinum toxin can be used in a wide range of applications, including wrinkle removing agents, agents for treating spastic hemiplegia and cerebral palsy, etc. Thus, the demand for type A botulinum toxin has increased, and studies on methods of producing botulinum toxin so as to satisfy the demand have been actively conducted.
A current typical commercial product is BOTOX® (a purified neurotoxin complex of type A botulinum toxin) that is commercially available from Allergan, Inc., USA. A 100-unit vial of BOTOX® is composed of about 5 ng of a purified neurotoxin complex of type A botulinum toxin, 0.5 mg of human serum albumin and 0.9 mg of sodium chloride and is reconstituted using sterile saline without a preservative (injection of 0.9% sodium chloride). Other commercial products include Dysport® (a complex of Clostridium botulinum type A toxin and hemagglutinin, which has lactose and human serum albumin in a pharmaceutical composition comprising botulinum toxin and is reconstituted using 0.9% sodium chloride before use) that is commercially available from Ipsen Ltd., UK, MyoBloc® (an injectable solution (a pH of about 5.6) comprising botulinum type B toxin, human serum albumin, sodium succinate and sodium chloride) that is commercially available from Solstice Neurosciences, Inc.
A medium for culture of Clostridium botulinum, which is generally used in a method for production of botulinum toxin as disclosed in Korean Patent No. 10-1339349, comprises animal components. Thus, if an animal abnormal prion known as an agent that causes transmissible spongiform encephalopathy is contained in the animal components due to contamination, it poses problems in a process for producing botulinum toxin.
Transmissible spongiform encephalopathy (TSE) is known as a neurodegenerative disorder causing serious degeneration of neurons, and examples thereof includes bovine spongiform encephalopathy (BSE), Scrapie, Creutzfeldt-Jakob disease (CJD), Gerstmann-Straussler-Scheinker syndrome, Kuru, transmissible mink encephalopathy, chronic wasting disease, feline spongiform encephalopathy, etc., which affect humans and animals. It was reported that BSE crosses the species barrier and infects even humans.
The agent that causes transmissible spongiform encephalopathy (TSE) has characteristics in that it has no immunogenicity and the incubation period is long. From histopathological analysis of BSE-affected bovine brain tissue, it can be seen that special spongiform vacuoles were formed in the brain due to damage to neurons and deposition of abnormal protein fibers.
The cause of TSE is a proteinaceous infectious particle known as the abnormal prion. Unlike general viruses that require nucleic acid, the abnormal prion is an infectious particle composed of protein alone without containing nucleic acid. Regarding TSE, it is known that, when an abnormal prion (PrPsc) that is an infectious particle binds to a normal prion (PrPc), it is converted to a pathogenic prion which is then accumulated in the brain (Prusiner SB, Alzheimer Dis Assoc Disord., 3:52-78, 1989).
Creutzfeldt-Jakob disease is a rare neurodegenerative disorder of human transmissible spongiform encephalopathy (TSE) where the transmissible agent is apparently an abnormal isoform of a prion protein. An individual with Creutzfeldt-Jacob disease can deteriorate from apparent perfect health to akinetic mutism within six months. Thus, a potential risk may exist of acquiring a prion mediated disease, such as Creutzfeldt-Jacob disease, from the administration of a pharmaceutical composition which comprises a biologic, such as a botulinum toxin, obtained using animal-derived products. Thus, if a pharmaceutical composition is prepared by drug substance produced using animal-derived components, it can subject the patient to a potential risk of receiving various pathogens or infectious agents.
Under this technical background, the present inventors have found that, when a medium comprising transmissible spongiform encephalopathy (TSE)-free plant-derived peptone, mineral components and TSE-free casein hydrolysate (e.g., TSE-certificated casein hydrolysate) is used for culture of Clostridium botulinum in order to prevent the risk of developing the above-described prion-mediated disease, the risk of development of the prion-mediated disease that can occur in a medium that is in current use (original medium) can be excluded, and the growth rate of Clostridium botulinum in the medium can be increased compared to that in the medium that is in current use and the plant-derived peptone-containing medium, thereby completing the present invention.